Various studies have described a highly specialised language as a subset or subsystem of the
general language (Harris, 1968: 152), a jargon (Bross, Shapiro, & Anderson, 1972: 1303) or a
sublanguage (Sager, 1986: 2; DeVille, 2001 : 5 and McEnery & Wilson, 1996: 166). One form of
language that often been considered as a sublanguage is the clinical language of the
health care domain. Different studies have defined a sublanguage on the basis of features such
as specialised subject matter, specific community, the speaker communicative purpose and
domain-specific lexis and syntax. McEnery & Wilson (1996: 166), on the other hand, suggest that
a sublanguage should be defined based on having a high degree of closure at various levels of
description. This study replicates and expands on McEnery & Wilson 's investigation. The prime
aim is to measure the degree of closure of the nursing textbooks and journals in order, first, to
determine whether these two restricted forms of clinical language can be rightly categorised as
a sublanguage; second, to understand better the linguistic features of the language of the
nursing domain; and finally, to better understand the nature of sub language. The nursing
textbook and journal corpora are compared to weather reports and the BNC Sampler. Like
clinical language, weather reports have been classified as a sub language in many studies (for
example Kittridge, 1982: 116). It is hypothesised that the weather reports and the nursing
textbooks and journals represent sub languages and that the BNC Sampler, on the other hand,
represents unrestricted language. Besides, measuring closure at lexical, morphsyntactic and
constituent levels, this study extends McEnery & Wilson's (1996) methodology to an examination
of n-gram closure. The findings show that none of the linguistic inventories of these corpora
approach closure at all levels; the nursing textbooks and journals seem to belong in a middle
area between highly constrained language and highly unconstrained language. The idea of
'sublanguage' is, thus problematic. The original definition of a sublanguage suggests a clear
division between sublanguage and unconstrained language. However, the findings of this study
seem to show that there is no explicit or clear-cut boundary; rather, the concept of
sublanguage should be on a continuum, with constrained language/sublanguage and
unconstrained languages at the two extreme ends, and the position of particular types of
language an effect, in part, of genre.